1. Field of the Invention
Embodiments of the invention generally relate to phase fraction meters such as water cut meters, and more particularly to an infrared optical phase fraction meter.
2. Description of the Related Art
Oil and gas wells often produce water along with hydrocarbons during normal production from a hydrocarbon reservoir within the earth. The water resident in the reservoir frequently accompanies the oil and/or gas as it flows up to surface production equipment. Operators periodically measure the fractions of an overall production flow stream that are water/oil/gas for purposes such as improving well production, allocating royalties, properly inhibiting corrosion based on the amount of water and generally determining the well's performance.
In many cases, several wells connect to a manifold in order to selectively isolate one of the wells and measure phase fractions of the production flow from that well. The manifold enables the flow from the well isolated from the combined flow to be diverted and either measured with a phase fraction meter without separation or sent to a separator where the individual production of oil, water, and gas are subsequently measured. In some cases, two phase separators divide the gas from the combined oil and water stream. In this scenario, flow meters measure the gas stream and the combined liquid production stream. In addition, the operator must obtain the percentages of the oil and water in the combined liquid stream to determine net oil and water production. This typically requires the time-consuming and expensive process of manual sampling or the use of an online device called a water cut meter.
As an alternative to the two phase separator, a three phase separator isolates the gas, oil and water so each phase can be metered independently. However, the three phase separator occupies a considerably larger space than the simpler two phase separators and is more expensive to own and operate. Further, inefficient separation or the propensity of certain oils to bind water in a tight emulsion still necessitates manual sampling in the oil and water legs.
Conventional water cut meters include capacitive water cut meters, density water cut meters, and microwave water cut meters. However, capacitive, density and microwave water cut meters each possess particular limitations. In general, these limitations include detection of oil-water concentrations only within a limited range, calibration difficulties, high costs, and results affected by the presence of gas bubbles, salinity fluctuations and density changes or close densities of oil and water.
Additionally, various infrared optical sensors enable water cut measurements. These infrared optical sensors overcome some of the limitations associated with other types of water cut meters. However, problems such as non-absorbance based signal attenuation and low water cuts can prevent accurate measurements using the infrared optical sensors.
Thus, there exists a need for an improved phase fraction meter. There exists a further need for an infrared optical phase fraction meter that minimizes measurement errors and enables accurate measurement across a full range of water cut. A still further need exists for an infrared optical phase fraction meter capable of measuring a water/oil ratio even in the presence of small levels of a third phase such as a free gas.